Production and use of hydrous titanium oxide



patented Nov. 9, 1943 PRODUCTION AND USE OF HYDROUS TITANIUM OXIDEAndrew T. McCord, Collingswood, and Harold F. Saunders, Haddonfield, N.1., assignors to The Sherwin-Williams company of Ohio N Drawing.

17 Claims.

This invention relates to the preparation of titanium pigments, andparticularly .to the preparation of nuclear solutions and seed crystalsand their use in the precipitation of titanium com-' pounds byhydrolysis at elevated temperatures of sulphuric acid solutionscontaining titanium.

- Titanium dioxide pigments are most commonly Company, Cleveland, Ohio,a.

Application February 1, 1941, Serial No. 377,046

precipitated from titanium sulphate solutions I which have been preparedfrom the reaction product of a titanium-bearing material such asilmenite ore and sulphuric acid. The preparation of such solutions iswell known in the artandhas been described by 'Blumenfeld in U. S.Patent No. 1,504,669 and by others.

The solution obtained by leaching the digestion mass with water is firsttreated with suililcient metallic iron to reduce all of the iron Presentto the ferrous state and then chilled to crystallize out the majorportion of the iron present as the sulphate. The solution at this stagemay contain around 9% to 13% of TiOz.

and is then customarily submitted to a vacuum concentration, process tobring the T102 content up to 15% to 16%.

This solution may then be hydrolyzed by boiling, but it is customary toassure the presence of a nuclear material in the solution, prior to anyactual precipitation of the TiOz by boiling, for the purpose ofaccelerating the rate of hydrolysis, increasing the yield andcontrolling the physical characteristics of the precipitated particles.This nuclear material may be formed in situ in the tion pattern, thebands not corresponding in position to either the characteristicposition of rutile or ana'tase lines. The characteristic positions 01"the bands and lines are shown in the following table:

Bands of s Lines of Lines of 235 anatase rutile i. U. A. U. A. U. 5. 833. 49 3. 24 3. 99 2. 37 2. 48 3; 145 1. 883 2. 29 2. 600 1. 695 2. 182.132 1. 655 2. 04 1. 888 1. 477 1. 685 1. 499 1. 358 1. 617 1. 354 1.334 1. 470 1. 177 l. 261 1. 44B 956 1. 161 1. 351 868 1. 044 1. 240743 1. 015 1. 167 951 1, 144 913 1. 092 892 876 843 824 806 In thecopending application Serial No. 370,486, filed Dec; 17, 1940 (Patent2,326,157, issued Aug. 10, 1943), to which this application alsorelates, a table is set forth extending'the characteristic lines of'y-titanic acid and including the relative densities of these lines.

' a It will then be understood that in this specisolution by dilutionunder rigidly controlled conditions, or added as a separatelypreparedseeding material.

In the prior art, titanium dioxide produced from the precipitateresulting from the hydrolysis at elevated temperatures of acrystalloidal solution of titanium insulphuric acid in the presence ofan adequate amount of colloidal TiOz com.-

. pound, as seeding material, after suitably washing, treating, andcalcining, has been the anatase modification, I

In our copending application, Serial No. 356,- 646, to which thisapplication is related, r e have shown that when a specific type oftitanium compound which we have termed 'y-titanic acid is added to thesulphuric acid solution of titanium as a nucleating agent, theprecipitate obtained by thermal hydrolysis may be calcined to the rutilemodification at temperatures between 800- 1000 C. I

In that application, -tit'anic acid-is defined as a form of hydroustitanium oxide characterized 1 as producing upon X-ray analysis a banddifiracfication and in the claims of this application the term -ytitanic acid is used to denote a compound of titanium so defined.

;Application Serial -Nos. 356,646 and 370,486 further describe severalmethods by which 'y-titanic acid maybe prepared.

We have now found that the hydrous titanium compound termed 'y-titanicacid may be converted to a specific compound which produces upon X-rayexamination a band difiraction pattern characteristic of anatase, butdiffering from the hydrous titanium compound obtained by thermalhydrolysis of sulphuric acid solutions of ilmenite and which alsoproduces upon X-ray a band diffraction pattern of anatase by its abilityto calcine to the rutile modification at a temperature between 800-1000C., while the lather at calcination temperatures up to 1000 C. producesonly anatase. We have further found that when our specific hydrous oxideof the anatase crystal structure is added to ilmenite solution as anucleating agent prior to hydrolysis, all of the precipitate obtained byhydrolysis will be 56 of ,a type correspondingto the seeding material inthat it, too, while showing the band pattern of anatase upon X-rayexamination, may be calcined to rutile at temperatures between 800 1000C. We have further found that when a sulphuric acid solution of titaniumnucleated with the anatase derived from- 'y-titaliic acid is hydrolyzedin the presence of anhydrite or other extender pigment, the precipitate,upon suitably washing, treating, and calcining will be a titaniumextended pigment in which thetitanium content is present as the rutilemodification.

We are aware that a specific hydrous form of titanium compound whichwould show upon X-ray examination a band pattern characteristic ofanatase and which would calcine to rutile at a temperature of 1000 C.was reported by Weiser and Milligan and described in their article X-raystudies on the hydrous oxides IV" in the J. Phys. Chem. 38, 513 (1934)by contactin a hydrochloric acid solution of titanium tetrachloride withaqua ammonia and boiling the amorphous precipitate obtained, but it wasnot known or disclosed that such a compound could be used as anucleating agent for ilmenite solu-, tion to produce a productreadily/convertible into We have now discovered that when anatasederived from 'y-titanic acid is used as nucleatin or seeding material inthe hydrolysis of sulphuric acid solutions containing titanium,'the T102precipitate will upon calcination be converted into rutile form at theusual calcination temperatures of between 800 C. and 1000 C.

By means of our invention we are able to obtain:

band difiractionpattem characteristic of anatase and which may becalcined to rutile at a temperature between 800-1000" C. by bydrolyzingan 11- menite solution containing as a nucleating agent a specifictitanium compound showing an X-ray dliiraction band pattern of anatase,which is derived from y-titanic acid and which may in itselfbeobcaalcined to rutile at temperatures between 800- 1 C.

(d) A precipitate which may be calcined to titanium extended pigmentwherein the titanium content is in the rutile modification and obtainedby the use of a -y-titanic acid or .a titanium compound derived from'y-titanlc acid, which shows an X-ray difiractlon pattern of anatase,and

'which may in itself be calcined to rutile at a temperature between800-1000" C. for nucleating 6 an ilmenite solution, and the hydrolysisof such nucleated ilmenite solution in the presence of anhydrite orother extenders.

(e) A pure titanium dioxide by performing the steps above referred tounder (d) and wherein the extender pigment is a minor amount of calciumsulphate, and from which the calcium sulphate is removed by washingprior to calcination.

An important part of our process is the separation of the precipitateobtained by contacting a mineral acid solution of titanium with ammoniaor other alkali from the soluble products of reaction or'from excessresidual acids in order that the 'y-titanic acid structure may develop.-Numerous patents have been issued wherein the pH of an ilmenite solutionwas lowered by addition of arr-alkali, thereby forming in situ acolloidal titanium compound with seeding propcities. This solutionwithout removal of excess sulphuric acid, when added to a furtherquantity of ilmenite solution, efiected acceleration of hydrolysis andimprovement in yield upon boiling, but the precipitate after suitablywashing, treating, and calcining, gave only anatase. Without wishing tobe bound in any way by our theories, we believe this condition resultsbecause the specific type of crystallinity characterized as 'y-titanicacid had not been allowed to develop and does not satisfactorily developin the presence of certain electrolytes. We have found that completeseparation from such reaction products and residual acids is notnecessary, but at least a major portion must be removed, otherwise therutile-forming properties are not adequately obtained.

Conversion of tiumic acid to anatase by boiling and by low temperatureheating ammonia with agitation. The ratio of 20% aqua ammonia to TiOzwas 35:1. The precipitate ob tained was thoroughly washed and boiled inan aqueous suspension with three times its weight of water for 1 hour..X-ray examination then showed a band pattern characteristic of'y-titanic acid. (la) Boiling of the slurry was continued for a furtherperiod of five hours, and X-ray examination then gave the pattern ofanatase.

. (117) A portion of the sample taken after the 1 hour boiling andshowing the 'y-titanic acid structure was dried and heated for 6 hoursat 184 C. Examination then showed the pattern of anatase. A temperatureas high as 800 C. may be employed for a shorter time with equivalentresults of producing anatase. The 'y-titanic acid obtained fromprecipitation or fluoride solution of titanium is, therefore, moreresistant to boiling than the precipitate from hydrochloric solution,but the change eventually does occur upon boiling. The anatases 1a andlb were then separated from excess water, treated with MgS04 (calculatedas 0.2% Mg( by weight to the weight of T10: present), as claimed incompanion ap plication Serial No. 367,390, filed Nov. 27, 1940 (Patent2,326,132, issued Aug. 10, 1943) dried and calcined for four hours at900 C. The product in both cases was pigmentary rutile, of high tintingstrength, whiteness and brightness, and of smooth texture.

Example 2.A sample of hydrous titanium oxide from thermal hydrolysis ofihnenite solu-' tion, showing an anatase band pattern, was dispersed inan equal weight or 96% sulphuric acid. diluted to twice its volume withwater, and sufilcient metallic zinc added to convert the titanium to thetitanous form. One volume of the reduced dispersion was slowly pouredinto four volumes of 20% aqua ammonia andthe heavy dark blue precipitateobtained was then oxidized by adding sumcient hydrogen ,peroxide todestroy the blue color. The precipitate was then 7 a slightly yellowishwhite. The precipitate was could be detected in the filtrate. X-rayexami- 1 nation of the hydrate thus obtained showed the band patterncharacteristic of -y-titanic,acid. This hydrate behaved similarly to thefluoride hydrate in that boiling in aqueous suspension for one hourshowed the 'y-titanic acid pattern, but prolonging the boil for afurtherfive hours showed conversion to anatase upon X-ray examination. The.hydrate was then separated from the excess water, dried, and calcinedfor two hours at 975 C. The tary rutile.

Example 3.-In a manner analogous to Example No. l,-an iron-free nitricacid solution of titanium and a sulphuric acid solution of titaniumcontaining 10%"1102 were precipitated with ammonia, washed, and given aboil in aqueous suspension for six hours. The hydrates obtained showedin both cases an anatase band pattern and were converted to rutile bycalcinati f r 2 hours at 975 C.

Conversion of 'y-iitam'c acid to anatase by thermal hydrolysis from asulphuric acid dispersum Example 4.-' -titanic acid was prepared bycontacting a solution of ammonium fluotitanate with aqua ammonia,thoroughly washing the precipitate andiboiling in water for on hour asin Example 1. The cake was dewateredto TiOz andthen air-dried to 75%Ti0z. 100 grams of this cake, equivalent to 75 grams TiOz was heated to70 C. with 90 grams H2804 and 275 rams of water. The mixture wasfiltered and heated to a boil for 1 hour. The titanium was completelyprecipitated, and upon separating and washing until the filtrate wassubstantially free from H2804, and dewatering, showed upon X-rayexamination a distinct band diffraction pattern of anatase. This hydrousoxide upon calcination for one hour at 950 C. gave a T102 which showed apattern, the'lines of which were substantially only those of rutile.

Example 5.-It was found upon experiment that the 'y-titanic acidsobtained by precipitation of other fluoride solutions of titanium,nitric acid solutions of titanium, hydrochloric acid solutions oftitanium, and sulphuric acid solutions of titanium with ammonia, analkali metal oxide, hydroxide, or carbonate, or group II oxides,hydroxides, or carbonates were also converted to anatase by dispersionin sulphuricacid and subsequent hydrolysis and treating in the samemanner as described in Example 4, and were further convertible to rutileby calcination at temperatures' between 850 and 950 C. for short periodsof one to two hours.

The preparation-of a hydrous oxide of anatase structure which may beconverted to rutile at temperatures below 1000" C. by thermal hydrolysisin the presence of sulphate ions is believed v to be entirely novel andis unexpected in view of the commercial practice of thermallyhydrolyzing sulphate solutions of titanium, in which case the anataseprecipitate obtained retains the anatase crystalline structure, althoughcalcined for many hours at 1000 C. Without being in any way bound by ourtheory, wg-explain thi unexpected result as due to the inherent abilityof the -titanic acid, once formed, to retain its characteristics eventhough redispersed in and thermally hydrolyzed from sulphuric acid. ,I

Nucleation of ilmenite solutzhns with anatase derived from 'y-titanicacid Example 6.'A quantity of moist anatase cake prepared .from -titanicacid by boiling in aqueous suspension as in Example la and containing38% T10: was heated with an edual weight of product was pigmen- 93%sulphuric acid until a clear, viscous mass was obtained. Sufllcientwater was added about 25% of its weight) to somewhat reduce the consist-A quantity of this diluted dispersion ency. equivalent to 1.4 grams ofT102 was added to one kilo of ilmenite solution containing 13.2% T102and 23.0% msol, and the mixture was boiled for five hours. The yield ofTiOz precipitated was slightly over 95%. The precipitate was separatedand washed until free from iron.- The wet cake containing 33% TiOz wasmixed with 1% HF (based on TiOz) and calcined .for two hours at 975 C;The product was of good pigmentary properties and X-ray'examination'showed'the diffraction pattern .of rutile.

Example 7.-A quantity of the anatase cake prepared as in Example lb(except that the time of drying the 'y-titanic acid was 700 C. for 1hour) was dispersed in 2.5 times its weight of 93% sulphuric andotherwise carried through the procedure as in Example 6; A- rutile ofsimilar characteristics was obtained.

Example 8.-A quantity of the moist cake obtained by dispersion of'y-titanic acid in sulphuric acid followed by hydrolysis and washing ofthe precipitate as in Example 4 and containing 35% TiOz was redispersedin an equal weight of 93% sulphuric acid. This dispersion was used inthe same manner as described under Example 6 for the nucleation ofilmenite solution, followed by hydrolysis, washing, treating,dewatering, and calcination to produce a rutile pigment.

Any of the anatase products described in the previous section, and of'y-titanic origin, may be used in preparing rutile pigment, byprocedures as Examples 6 to 8.

The wet cake produced in Examples 6, 7 and 8 i may be used fornucleating an ilmenite solution to produce more ofthe same cake.

Nucleation of ilmenite solutions with anatase derived from 'y-titanicacid and hydrolysis in the presence of an'ea'tender pigment Thefollowing single example is given as illustrating this type of process.It will be understood that any of the anatases derived from-y-titanic800 C. The titanium oxide at thispoint showed 100 grams of this a bandpattern of anatase. anatase was heated with 270 grams of 93% sulphuricacid until a clear, viscous mass resulted. This was diluted with 25% ofwater to produce a somewhat thinner consistency. A quantity of thisliquid containing 1 gram of TiO: was added to an ilmenite solutioncontaining 100 grams of T102 and analyzing 8.3% T102 and 19% H2804.This-seeded solution was added to a slurry of calcium sulphate inanhydrite form obtained by product to be equal suspending 240 grams oi.dry anhydrite in 800 grams of water. The mixture was boiled for 3 hours.The precipitate was separated and washed with liters ofwater. The ratioof CaSO4 to- TiOz was'then 70:30. The slurry was dewatered and mixedwith 0.2% MgSO; (calculated as MgO' on weight of TiOz) and calcined for2 hours at 975 C. The product was extremely white, excellent softtexture, possessed a tinting strength of 650. and X-ray examination ofthe titanium content (obtained by washing out the CaSOr with HNOa')showed the titanium to be present as rutile. I

It is also to be understood that the example above representing 70:30ratio CaS04 to TiOz is only representative, as ratios of Ti'Oz from 1 upto 100 are within the scope of the practice of this invention. I

From the foregoing examples it will appear that the new form of anatasewhich can be readily converted to rutile may be prepared by:

(a) Dispersing 'y-titanic acid in sulphuric acid and reprecipitating .byheating,

(1)) Boiling -titanic acid in water, and

(c) Drying -titanic acid and heating.

So. far as we have been able to determine, the

anatase prepared by all three such procedures was the same and they areidentical for the purpose of nucleating or seeding an ilmenite solutionto produce a hydrous titanium oxide having an anatase structure andwhich may be readily calcined to produce rutile.

The following tabulation demonstrates the superiorities of our pigment:Tinting strength determined by the ASTM Procedure D-332-36 "70:30 CaSOa.'y-anatase pigment by prior art (high grade commercially availableHiding power Hiding power as square feet per pound of pigment, wasdetermined according to ASTM Designation D-406-39, on the priorartpigments, and shows 48 sq. ft., while our 70:30'extended T102products showed from 55 to 65 sq. ft.

Color A- direct visual com arison in oil shows our superior to thehighest pigment, since formulation with CaSOrzTiOa extended pigments iscommon knowledge. Our products may be substituted pound for pound forprior art pigment with the improved results in hiding, color,brightness, etc., previously noted.

Example 10.-'y-titanic acid was prepared by dissolving titaniumtetrachloride in twice its volume of water and slowly adding thismixture to four times its volume of aqua ammonia. The precipitate waswashed until the filtrate was substantially free from ammonia. A smallsample at this point was air dried at 60 C. and an X-ray diffractionpattern was typical 0! '7- titanic acid. The wet hydrate was slurried inwater to contain approximately 5% T10: and boiled for six hours. Theslurry was dewatered.

\ A small portion was air dried at 60 C. and showed solution containing8.1% TiOz and 19% H2805.

the typical anatase X-ray diifraction band pattern. The wet cake,containing 30% T102, was redispersed in an equal weight of sulphuricacid. An amount of this dispersion equivalent to one gram of T102 wasadded to 1,250 grams of elmenii'e This nucleated ilmenite solution wasadded to a slurry of anhydrite in water containing 235 grams CaSOr, 180grams H2804, and 820 grams of wa-' ter. The mixture was boiled fourhours to complete the thermal hydrolysis of the titanium. The solidswere separated and washed until the filtrate was iron-free, dewateredand calcined 2 hours at 975C. The product was a titanium extendedpigment containing approximately 70% CaSO4 and 30% T102, and in whichthe titanium content was present substantially as rutile.

Certain of the subject matter disclosed in this application as filed hasbeen divided out and is claimed in our copending applications SerialNos. 441,532 and 441,538, filed May 2, 1942.

Having thus described our invention, what we" claim as new and desire tosecure by Letters Patent is: i

1. The process of forming anatase which includes boiling a sulphuricaciddispersion of y-tiacid and reprecipitating by heating to a tenigrades:30 CaSOr anatase extended pigments available and to possess a superiorretention of color on exposure to atmospheric condition in paint film.

Because of the greater hiding power, further extension of rutile'pigments in paint formulation is possible with our pigments, to obtainhiding power equal to prior art pigments.- Besides economy, anotheradvantage of this lies inability to obtain considerably further'flatting effects in flat paint formulation, since flatting is inconsiderable measure increased with increasing proportion of inertpigments.

It would not appear necessary to present detail paint formulations,illustrating usage 0! our tanic acid.

2. The process of forming a hydrous titanium 'oxide having the anatasestructure whichincludes dispersing of 'y-titanic acid in sulphuricperature from about C. to about the boiling temperature of thedispersion.

3. The'process of forming a hydrous titaniumoxide having the anatasestructurewhich includes precipitating ammonium fluotitanate with aquaammonia, separating the precipitate as 'y-titanic acid, and heating saidprecipitate in a sulphuric acid dispersion.

4. The process of forming a hydrous titanium oxide having the anatasestructure which includes precipitating ammonium fluotitanate with aquaammonia, separating the precipitate as 'ytitanic acid, drying theprecipitate and heating in a sulphuric acid solution.

5. The process of forming a hydrous titanium oxide having the anatasestructure which includes precipitating ammonium fluotitanate with aquaammonia, separating the precipitate as 'ytitanic acid, dispersing theprecipitate in sulphuric acid and reprecipitatingJay heating to atemperature between about 90 C. and-the boiling point. I

6. The process of producing a hydrous titanium structure and which oxidehaving the anatase may. h c lgined to rutile, which processincludesseeding an ilmenite solution with a small amount of the hydrous titaniumoxide prepared by the solution.

aceaeat process defined in claim 2 and hydrolyzing said 7. The processof producing a hydrous titanium oxide having the anatase structure andwhich may be calcined to rutile, which process includes seeding anilmenite solution with a small amount of anatase identical with thatobtained by heating 'y-titanic acid in sulphuric acid.

8. The process of making rutile which includes heating -titanic acid ina sulphuric acid dispersion until a hydrous titanium oxide having ananatase structure has developed and calcining said hydrous titaniumoxide at a temperature between 800 C. and about 1000 C. i

9. The process of producing rutile which includes seeding an ilmenitesolution with a small amount of anatase identical with that obtained byboiling a sulphuric acid dispersion of 'y-titanic acid, hydrolyzing saidsolution, separating the precipitate and calcining it at a temmraturebetween about 800 C. and about 1000 C.

10. The process of making an extended pigment which includes nucleatingan ilmenite solution with anatase identical with that resulting fromboiling a sulphuric acid dispersion of 'y-titanic acid and hydrolyzingsaid solution in the presence of calcium sulphate.

ll. The process of making a pigmentary rutile which includes nucleatingan ilmenite solution with anatase identical with that derived from'ytanic acid by heating a. dispersion thereof. in sulphuric acid,hydrolyzing said solution in the presence of calcium sulphate, washingout the calcium sulphate from the precipitate, and calcining.

12. The process of making an extended pigment which includes nucleatingan ilmenite solution with anatase identical with that prepared byheating a sulphuric acid dispersion of 'y-titanic acid obtained fromprecipitation of ammonium fluotitanate with ammonia, hydrolyzing saidsolution in the presence of an extender, separating, washing andcalcining the precipitate.

13. The process which includes heating a sulill) phuric acid dispersionor q-titanic acid at between C. and boiling to produce a hydroustitanium oxide having anatase structure, separating the precipitate,redispersing said hydrous titaniumoxide in sulphuric acid, adding saiddispersed hydrous titanium oxide to an ilmenite solution as a nucleatingagent, hydrolyzing said solution to form a precipitate, separating theprecipitate, washing and calcining it.

14. The process which includes heating a sulphuric acid dispersion of-titanic acid to produce a hydrous titaniumbxide having anatasestructure, redispersing said hydrous titanium oxide in sulphuric acid,adding said dispersed hydrous titanium oxide to an ilmenite solution asa nucleating agent, hydrolyzing said solution to form a precipitate inthe presence of an extender, separating the precipitate, washing andcalcining it.

15. The process of forming a hydrous titanium oxide having the anatasestructure which includes precipitating a titanium solution by the actionof ammonia in the presence of a compound selected from the groupconsisting of the oxides,

hydroxides and carbonates of alkali metals and metals of group II,dispersing the precipitate in sulphuric acid, and reprecipitating byheating.

16. The process of producing rutile which includes boiling a sulphuricacid dispersion of 7- titanic acid to form a hydrous titanium oxidehaving an anatase structure, seeding an ilmenite solution with a smallamount of said hydrous titanium oxide, hydrolyzing said solution,separating the precipitate, and calcining it at a temperature between800 C. and about 1000 C.

1'7. The process of making an extended pigment which includes nucleatingan ilmenite solution with anatase identical with that prepared byheating a sulphuric acid dispersion of 7-111- tanic acid, hydrolyzingsaid solution in the presence of an extender, separating, washing andcalcining the precipitate.

ANDREW T. McCORD. HAROLD F. SAUNDERS. I

